What are the summer management measures for walnut trees?

SummaryFlower and fruit retention: thin out the vigorously growing female flowers, then carry out supplementary artificial pollination. Fertilization: during the vigorous growth period of female flowers, spray gibberellin, boron fertilizer and urea once every 15 days. Branch bending: pull the upturned branches into position. Pest and disease control: for rot disease, apply carbendazim wettable powder; for black spot disease, spray Bordeaux mixture; for red spider mites, spray refined ketone mite clear, etc.

I. Flower and fruit retention of walnut trees

1. Flower and fruit thinning: in summer, management needs to be carried out according to the variety, tree vigor, tree age, soil conditions, etc.; thin out the vigorously growing female flowers sequentially from the inside out, from dense to sparse, and from bottom to top.

2. Artificial pollination: the first time can be when 10% of the female flowers are in full bloom and form an “inverted figure-eight” shape, carry out supplementary artificial pollination; the second time can be when 30% of the female flowers are in full bloom, carry out supplementary artificial pollination.

II. Fertilization of walnut trees

1. Topdressing: for walnut trees that have already set fruit, apply 150 grams of compound fertilizer plus 250 grams of urea after flowering; the compound fertilizer should be one with a high phosphorus content. For newly planted walnut trees and those bearing fruit on a trial basis, when the new shoots grow to 15cm, apply 50 grams of compound fertilizer plus 100 grams of urea.

2. Foliar spraying: during the vigorous growth period of female flowers, spraying gibberellin and boron fertilizer can increase the fruit-setting rate, and once every half a month, 0.3%-0.5% urea can be sprayed, which helps promote shoot growth and make the leaves greener and thicker. Topdressing and foliar spraying can generally be carried out at the same time or alternately.

III. Branch bending of walnut trees

Walnut trees need long-term branch bending. Generally, branches that were not bent in spring, or were not bent into position, should continue to be pulled into position; moreover, as branches elongate and upturn again, the upturned parts need to be pulled down promptly. Branches that were short-cut in spring, or new branches that have grown to 1 meter, should also be bent promptly.

IV. Pest and disease control of walnut trees

1. Common diseases of walnut trees include rot disease and black spot disease. During this period, management of the walnut orchard needs to be strengthened, organic fertilizer appropriately increased, and pruning carried out reasonably. The trunk can also be whitewashed. In summer and during the growing season, diseased spots should be scraped off promptly; after scraping, apply 50% carbendazim wettable powder 1000-fold solution, or 40% crystal lime sulfur 20-30-fold solution, or 5-10 Baume lime sulfur for control.

2. Black spot disease mainly damages leaves, branches and fruits. Generally, during the growing period, spray 1-3 times with 1:0.5:200 Bordeaux mixture, or 500-800-fold solution of Tuzet wettable powder and 50% thiophanate-methyl.

3. The common pest in summer is the red spider mite. Red spider mites generally harm the leaves, then absorb the tree's nutrients. The peak period is from mid-to-late August to September, which can cause leaf drop, dried-up leaves, and an increase in empty and shriveled shells, with yield dropping by about 50%. Therefore, timely control is needed. During control, in order to reduce the mite population density and control the peak period in August-September, pesticides such as refined ketone mite clear, abamectin, fenpyroximate and saomangjing can generally be used for spraying and killing.

V. Harvesting the fruit of walnut trees

1. In September, when 1/3 of the fruit skin has split open, harvesting can be carried out. When harvesting, a bamboo pole can be used to strike from the inside outward to prevent damaging the buds. After harvesting, walnuts whose skins have not separated can be piled indoors or outdoors to a height of 40-50cm, covered with 10cm-thick leaves or wheat bran, and peeled after waiting 3 days.

2. After peeling, the walnuts need to be washed clean with water, then placed on bamboo mats to drain off the water, and then dried in the sun. During this period, they should be turned promptly. Generally, after waiting 3-5 days they can be sun-dried. Sun-dried walnuts make a relatively crisp sound when knocked together, and the inner seed coat also peels off easily.